The present invention relates to a technology for manufacturing a semiconductor device, and particularly to a technology effective if applied to a method of manufacturing a semiconductor device having a nonvolatile memory, which is mounted on a system LSI (Large Scale Integrated Circuit) or the like.
As a general-purpose microcomputer equipped with a nonvolatile memory which continues to retain memory information even if power is turned off, may generally be mentioned an OTP (One Time Programmable) ROM (Read Only Memory) built-in microcomputer or a flash memory built-in microcomputer intended for a customer-based soft development or debugging, or a mask ROM built-in microcomputer intended for a cost reduction at mass production, or the like. Here, an OTPROM is a nonvolatile memory (inclusive of an EPROM (Erasable Programmable Read Only Memory)) capable of writing memory contents therein only once by a customer, a flash memory is a nonvolatile memory (inclusive of EEPROM (Electrically Erasable Programmable Read Only Memory)) capable of electrically effecting all of erasure/reprogramming of memory information, and a mask ROM is a program-fixed nonvolatile memory which writes memory information therein in a manufacturing process.
Incidentally, a technology for allowing a plurality of types of semiconductor elements to be formed on a sheet of semiconductor wafer and enhancing production efficiency of various kinds of semiconductors has been described in, for example, Unexamined Patent Publication Hei 7(1995)-283287 of Iwasaki et al.
Further, a simple manufacturing method of a semiconductor device, which is capable of effecting writing on a read only memory element of the semiconductor device having a flash memory element and a read only element together during a semiconductor device manufacturing process and carrying out reading even without writing after its commercialization, has been disclosed in, for example, Unexamined Patent Publication Hei 5(1993)-304277 of Yamamoto et al.
The present inventors have discussed a method of manufacturing a microcomputer having built therein a mask ROM as a nonvolatile memory. The following is a technology discussed by the present inventors, and its summary is as follows:
FIG. 8 is a process diagram showing one example of a fabrication process of the mask ROM built-in microcomputer discussed by the present inventors.
A program for the mask ROM is first developed by a customer (Step 100). This customer program is data-transmitted to a manufacturing site (Step 101). Next, the transmitted data is converted (Step 102). Further, a mask is fabricated based on the data (Step 103), and wiring patterns are formed on a base wafer (Step 104) fabricated in a wafer process (1) in advance, using the mask in a wafer process (2) (Step 105), whereby a prototype of a mask ROM built-in microcomputer is manufactured. Incidentally, test items, standards, etc. employed in a subsequent probe test and screening are also simultaneously created upon the data conversion in Step 102.
Next, whether mask ROM built-in microcomputers formed in individual chips on the wafer are non-defective or defective, is determined by a probe test (Step 106), and thereafter, a prototype is delivered to a customer (Step 107). The prototype is evaluated by the customer. When it is determined that no problem occurs in the corresponding mask ROM and the microcomputer with the mask ROM built therein (Step 108), an order for the fabrication of the mask ROM built-in microcomputer is formally forwarded to the manufacturing site (Step 109). Thereafter, wiring patterns are formed on the base wafer by use of the mask in the wafer process (2) (Step 110). Whether the mask ROM built-in microcomputers formed in the individual chips on the wafer are non-defective or defective, is determined by a probe test (Step 111). Afterwards, the non-defective mask ROM built-in microcomputers are assembled (Step 112) and their screening according to product standards is performed (Step 113), and each of the mask ROM built-in microcomputers each having satisfied the product standards is packed and shipped (Step 114).
Incidentally, when a problem on the program occurs in the corresponding mask ROM or the microcomputer with the mask ROM built therein upon the customer evaluation in Step 108, the program is discussed again by the customer and a mask ROM built-in microcomputer is prototyped and evaluated in a manner similar to the above process steps subsequently.
However, the following problems have become evident after the present inventors have discussed the method of manufacturing the mask ROM built-in microcomputer.
In the case of a mask ROM, a dedicated mask is fabricated based on a customer program and each wiring pattern is formed using the mask, whereby the customer program is written into its corresponding base chip. Therefore, the mask ROM has a problem in that a mask charge becomes a burden regardless of the produced number thereof, and a TAT (Turn-and Around Time) of a manufacturing process becomes long.
Since it is difficult to produce mask ROM built-in microcomputers in just proportion according to the number thereof by order, they are normally produced in excess of the required number thereof and thereafter the number of their shipments is adjusted according to customer""s requests. With a progress of an increase in the diameter of the wafer, however, the number of ordered mask ROM built-in microcomputers per company is supposed to become fewer than the number of mask ROM built-in microcomputers obtained from one wafer. In this case, there is fear that the original cost of each microcomputer product rises due to the unwanted mask ROM built-in microcomputers.
On the other hand, a microcomputer with a flash memory built therein as a nonvolatile memory grows in demand as well. However, a test process therefor increases in complexity as compared with the mask ROM built-in microcomputer, thus resulting in the occurrence of a problem that the TAT becomes long and its manufacturing cost rises. Therefore, a changeover from all of mask ROMs each having a microcomputer built therein to flash memories is considered to be difficult.
An object of the present invention is to provide a technology capable of achieving the shortening of a TAT of a microcomputer with a built-in nonvolatile memory.
Another object of the present invention is to provide a technology capable of reducing the cost of a microcomputer with a built-in nonvolatile memory.
The above, other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.
Summaries of representative ones of the inventions disclosed in the present application will be explained in brief as follows:
The present invention comprises the steps of: forming, in each chip lying within a wafer, a semiconductor device having a nonvolatile memory comprised of memory cells each substantially identical in structure to each of memory cells of a flash memory; bringing a probe into contact with each of electrode pads of the semiconductor device to thereby write memory information into the corresponding nonvolatile memory; and disabling rewriting of the memory information written into the nonvolatile memory, whereby the memory information written into the nonvolatile memories are made different for each wafer or every plural wafers, or for each chip in the wafer or every plural chips in the wafer to thereby form a plurality of types of nonvolatile memories different in specification from one another.
Further, the present invention comprises the steps of: forming, in each chip lying within a wafer, a semiconductor device having a nonvolatile memory comprised of memory cells each substantially identical in structure to each of memory cells of a flash memory; converting a program developed by a customer into data; writing memory information into the corresponding nonvolatile memory in a probe test process and thereafter probe-testing the semiconductor device having the nonvolatile memory; passivating an erase circuit and a write circuit to thereby disable rewriting of the memory information; assembling the semiconductor devices each having the nonvolatile memory; and screening the semiconductor devices each having the nonvolatile memory, whereby the memory information is directly transferred to a probe test device, based on instructions given by a production management system after the conversion of the program developed by the customer into the data.